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Spray modeling techniques have evolved from the classic DDM (Discrete Drops Method) approach, where the continuous liquid jet is discretized into “drops” or “parcels” till advanced spray models often based on Eulerian approaches. The former technique, although computationally efficient, is essentially inadequate in highly dense jets, as in the near nozzle region of compression ignition engines, while the latter could lead to extreme levels of computational effort when resolved interface capturing methods, such as VoF (Volume of Fluids) and LS (Level-Set) types, are used. However, in a typical engineering calculation, the mesh resolution is considerably coarser than in these high fidelity computations. If one presumes that these interfacial details are far smaller than the mesh size, smoothing features over at least one cell ultimately results in a diffuse-interface treatment in a Eulerian framework.

In the present paper the results of an experimental and numerical analysis of a common-rail, high pressure Diesel spray evolving in high counter pressure conditions is reported. The experimental study was carried out mainly in terms of spray momentum flux indirect measurement by the spray impact method; the measurement of the impact force time-histories, along with the CFD analysis of the same phenomenon, gave interesting insight in the internal spray structure. As well known, the overall spray structure momentum flux along with the injection rate measurements can be used to derive significant details about the in-nozzle flow and cavitation phenomena intensity. The same global spray momentum and momentum flux measurement can be useful in determining the jet-to-jet un-uniformities also in transient, engine-typical injection conditions which can assist in the matching process between the injection system and the combustion chamber design.

Radio Frequency Corona ignition systems represent an interesting solution among innovative ignition strategies for their ability to stabilize the combustion and to extend the engine operating range. The corona discharge, generated by a strong electric field at a frequency of about 1 MHz, produces the ignition of the air-fuel mixture in multiple spots, characterized by a large volume when compared to a conventional spark, increasing the early flame growth speed. The transient plasma generated by the discharge, by means of thermal, kinetic and transport effects, allows a robust initialization of the combustion even in critical conditions, such as using diluted or lean mixtures. In this work the effects of Corona ignition have been analyzed on a single cylinder optical engine fueled with gasoline, comparing the results with those of a traditional single spark ignition.

In the last decades, worldwide automotive regulations induced the industry to dramatically increase the application of electronics in the control of the engine and of the pollutant emissions reduction systems. Besides the need of engine control, suitable fault diagnosis tools had also to be developed, in order to fulfil OBD-II and E-OBD requirements. At present, one of the problems in the development of Diesel engines is represented by the achievement of an ever more sharp control on the systems used for the pollutant emission reduction. In particular, as far as NOx gas is concerned, EGR systems are mature and widely used, but an ever higher efficiency in terms of emissions abatement, requires to determine as better as possible the actual oxygen content in the charge at the engine intake manifold, also in dynamic conditions, i.e. in transient engine operation.

Water injection in highly boosted gasoline direct injection (GDI) engines has become an attractive area over the last few years as a way of increasing efficiency, enhancing performance and reducing emissions. The technology and its effects are not new, but current gasoline engine trends for passenger vehicles have several motivations for adopting this technology today. Water injection enables higher compression ratios, optimal spark timing and elimination of fuel enrichment at high load, and possibly replacement of EGR. Physically, water reduces charge temperature by evaporation, dilutes combustion, and varies the specific heat ratio of the working fluid, with complex effects. Several of these mutually intertwined aspects are investigated in this paper through computational fluid dynamics (CFD) simulations, focusing on a turbo-charged GDI engine with port water injection (PWI). Different strategies for water injection timing, pressure and spray targeting are investigated.

Emission legislation for passenger cars is requiring a drastic reduction of exhaust pollutants from internal combustion engines (ICE). In this framework, achieving a quick heating-up of the catalyst is of paramount importance to cut down the cold start emissions and meet future regulation requirements. This paper describes the development and the basic characteristics of a novel burner for gasoline engines exhaust systems designed for being activated immediately at engine cold start. The burner is comprised of a fuel injector, an air system, and an ignition device. The design of the combustion chamber is first presented, with a description of the air-fuel interactions and mixture formation processes. Swirl is used along with a flame-holder concept to anchor the flame at the mixer exit. Spray-swirl and spray-walls interaction are also discussed. Computational Fluid Dynamics (CFD) analyses have been used to investigate these aspects.

Natural gas (NG) is an alternative fuel for spark-ignition engines. In addition to its cleaner combustion, recent breakthroughs in drilling technologies increased its availability and lowered its cost. NG consists of mostly methane, but it also contains heavier hydrocarbons and inert diluents, the levels of which vary substantially with geographical source, time of the year and treatments applied during production or transportation. To investigate the effects of NG composition on engine performance and emissions, a 3D CFD model of a heavy-duty diesel engine retrofitted to NG spark ignition simulated lean-combustion engine operation at low speed and medium load conditions. The work investigated three NG blends with similar lower heating value (i.e., similar energy density) but different Methane Number (MN). The results indicated that a lower MN increased flame propagation speed and thus increased in-cylinder pressure and indicated mean effective pressure.

It has been proved that Radio Frequency Corona, among other innovative ignition systems, is able to stabilize combustion and to extend the engine operating range in lean conditions, with respect to conventional spark igniters. This paper reports on a sensitivity analysis on the combustion behavior for different values of Corona electric control parameters (supply voltage and discharge duration). Combustion analysis has been carried out on a single cylinder PFI gasoline-fueled optical engine, by means of both indicating measurements and imaging. A high-speed camera has been used to record the natural luminosity of premixed flames and the obtained images have been synchronized with corresponding indicating acquisition data. Imaging tools allowed to observe and measure the early flame development, providing information which are not obtainable by a pressure-based indicating system.

Among plasma-assisted ignition technologies, the Radio-Frequency (RF) corona family represents an interesting solution for the ability to extend the engine operating range. These systems generate transient, non-thermal plasma, which is able to enhance the combustion onset by means of thermal, kinetic and transport effects. Streamer-type RF corona discharge, at about 1 MHz, ignites the air-fuel mixture in multiple filaments, resulting in many different flame kernels. The main issue of this system is that at high electrode voltage and low combustion chamber pressure a transition between streamer and arc easily occurs: in this case transient plasma benefits are lost. A barrier discharge igniter (BDI), supplied with the same RF energy input, instead, is more breakdown-resistant, so that voltage can be raised to higher levels. In this work, a streamer-type RF corona igniter and a BDI were tested in a single-cylinder optical engine fueled with gasoline.

An extensive numerical study of two-phase flow inside the nozzle holes and the issuing jets for a multi-hole direct injection gasoline injector is presented. The injector geometry is representative of the Spray G nozzle, an eight-hole counter-bored injector, from the Engine Combustion Network (ECN). Homogeneous Relaxation Model (HRM) coupled with the mixture multiphase approach in the Eulerian framework has been utilized to capture the phase change phenomena inside the nozzle holes. Our previous studies have demonstrated that this approach is capable of capturing the effect of injection transients and thermodynamic conditions in the combustion chamber, by predicting phenomenon such as flash boiling. However, these simulations were expensive, especially if there is significant interest in predicting the spray behavior as well.

Ongoing development of a CFD framework for the simulation of primary atomization of a high pressure diesel jet is presented in this work. The numerical model is based on a second order accurate, polyhedral Finite Volume (FV) method implemented in foam-extend-4.1, a community driven fork of the OpenFOAM software. A geometric Volume-of-Fluid (VOF) method isoAdvector is used for interface advection, while the Ghost Fluid Method (GFM) is used to handle the discontinuity of the pressure and the pressure gradient at the interface between the two phases: n-dodecane and air in the combustion chamber. In order to obtain highly resolved interface while minimizing computational time, an Adaptive Grid Refinement (AGR) strategy for arbitrary polyhedral cells is employed in order to refine the parts of the grid near the interface. Dynamic Load Balancing (DLB) is used in order to preserve parallel efficiency during AGR.

A 1998 Toyota Corona passenger car with a direct injection spark ignition (DISI) engine was tested at constant engine speed (2000 rpm) over a range of loads. Engine-out and tailpipe emissions of gas phase species were measured each second. This allowed examination of the engine-out emissions for late and early injection. Seven fuels were used for these tests: five blended fuels and two pure hydrocarbon fuels. These seven fuels can be divided into groups for examination of the effects of volatility, MTBE, and structure (an aromatic versus an i-alkane). Correlations between the fuel properties and their effects on emissions are presented. Use of steady state tests rather than driving cycles to examine fuel effects on emissions eliminates the complications resulting from accelerations, decelerations, and changes of injection timing but care had to be taken to account for the periodic regenerations of the lean NOx trap/catalyst.

A 1998 Toyota Corona passenger car with a direct injection spark ignition (DISI) engine was tested over the Federal Test Procedure (FTP) driving cycle. Speciated engine-out hydrocarbon emissions were measured. Seven fuels were used for these tests: five blended fuels and two pure hydrocarbon fuels. One of the blended fuels was CARB Phase 2 reformulated gasoline which was used as the reference fuel. The remaining four blended fuels were made from refinery components to meet specified distillation profiles. The pure hydrocarbon fuels were iso-octane and toluene - an alkane and an aromatic with essentially identical boiling points. The five blended fuels can be grouped to examine the effects of fuel volatility and MTBE. Additionally, correlations were sought between the fuel properties and the Specific Reactivity, the exhaust “toxics”, and the pass-through of unburned fuel species.

A 1998 Toyota Corona passenger car with a direct injection spark ignition (DISI) engine was tested via a variety of driving cycles using California Phase 2 reformulated gasoline. A comparable PFI vehicle was also evaluated. The standard driving cycles examined were the Federal Test Procedure (FTP), Highway Fuel Economy Test, US06, simulated SC03, Japanese 10-15, New York City Cycle, and European ECE+EDU. Engine-out and tailpipe emissions of gas phase species were measured each second. Hydrocarbon speciations were performed for each phase of the FTP for both the engine-out and tailpipe emissions. Tailpipe particulate mass emissions were also measured. The results are analyzed to identify the emissions challenges facing the DISI engine and the factors that contribute to the particulates, NOx, and hydrocarbon emissions problems of the DISI engine.

Conventional spark-ignition engines are currently incapable of meeting rising customer performance demands while complying with even stringent pollutant-emissions regulations. As a result, innovative ignition systems are being developed to accomplish these targets. Radio-Frequency corona igniters stand out for their ability to accelerate early flame growth speed by exploiting the combined action of kinetic, thermal and transport effects. Furthermore, a volumetric discharge enables the promotion of combustion over a wide area, as opposed to the local ignition of traditional spark. The present work wants to evaluate the advantages of a Streamer-type Radio Frequency corona discharge at about 100 kHz with respect to those of traditional spark igniter.

Artificial Intelligence is becoming very important and useful in several scientific fields. Machine learning methods, such as neural networks and decision trees, are often proposed in applications for internal combustion engines as virtual sensors, faults diagnosis systems and engine performance optimization. The high pressure of the intake air coupled with the demand of lean conditions, in order to reduce emissions, have often close relationship with the knock events. Fuels autoignition characteristics and flame front speed have a significant impact on knock phenomenon, producing high internal cylinder pressures and engine faults. The limitations in using pressure sensors in the racing field and the challenge to reduce the costs of commercial cars, push the replacement of a hardware redundancy with a software redundancy.

In the present paper, a detailed numerical and experimental analysis of a spray momentum flux measurement device capability is presented. Particular attention is devoted to transient, engine-like injection events in terms of spray momentum flux measurement. The measurement of spray momentum flux in steady flow conditions, coupled with knowledge of the injection rate, is steadily used to estimate the flow mean velocity at the nozzle exit and the extent of flow cavitation inside the nozzle in terms of a velocity reduction coefficient and a flow section reduction coefficient. In the present study, the problem of analyzing spray evolution in short injection events by means of jet momentum flux measurement was approached. The present research was based on CFD-3D analysis of the spray-target interaction in a momentum measurement device.

The present paper describes the effect of thermal conditions on the hydraulic behavior of Diesel common rail injectors, with a particular focus on low temperatures for fuel and injector body. The actual injection system thermal state can significantly influence both the injected quantity and the injection shape, requiring proper amendments to the base engine calibration in order to preserve the combustion efficiency and pollutant emissions levels. In particular, the introduction of the RDE (Real Driving Emission) test cycle widens the effective ambient temperature range for the homologation cycle, this way stressing the importance of the thermal effects analysis. An experimental test bench was developed in order to characterize the injector in an engine-like configuration, i.e. fuel pump, piping, common rail, pressure control system and injectors.

In the present paper an innovative approach for the shot-to-shot hydraulic characterization of low pressure injection systems is experimentally assessed. The proposed methodology is an inverse application of the Zeuch’s method, which in this case is applied to a closed volume upstream the injector instead of downstream of it as in conventional injection analyzers. By this approach, the well-known constraint of having a finite volume pressurized with the injected liquid downstream the injector is circumvented. As a consequence, with the proposed instrument low pressure injectors - such as PFI, fed with gasoline or water, SCR injectors - can operate with the prescribed upstream-downstream pressure differential. Further, the injector can spray directly in atmosphere or in any ambient at arbitrary pressure and temperature conditions, allowing the simultaneous application of other diagnostics such as imaging, momentum flux measurement or sizing instruments.

In the current automotive scenario, particulate filter technology is mandatory in order to attain emission limits in terms of particulate matter for diesel engines. Despite the fact that the Diesel Particulate Filter (DPF) is often considered a mature technology, significant issues can result from the use of the engine fuel injectors to introduce into the exhaust pipe the fuel needed to ignite the particulate matter accumulated in the filter during its regeneration. The most important issue is lubricant oil dilution with fuel as a consequence of significant spray impact on the cylinder liner. As an alternative, the fuel required to start DPF regeneration can be introduced in the exhaust pipe by an auxiliary low-pressure injector spraying in the hot exhaust gas stream.